Secondary batteries are rechargeable and dischargeable by using an electrode material having excellent reversibility, and lithium secondary batteries have been commercialized representatively. Lithium secondary batteries are expected to be provided in moveable units such as vehicles or to be applied as medium and large sized power source used in a power storage of a power supply network such as a smart grid, as well as small sized power source of small information technology (IT) appliances such as smart phones, portable computers, and electronic paper.
When lithium metal is used as an anode material of a lithium secondary battery, dendrites may be formed, and thereby causing shorting of the battery or a risk of explosion. Thus, instead of using the lithium metal, crystalline carbon such as graphite and artificial graphite or carbon based active material such as soft carbon or hard carbon having a theoretical capacity of 372 mAh/g and capable of intercalating and deintercalating lithium ions has been mainly used as an anode. However, as applications of secondary batteries have increased, demands for secondary batteries having high capacity and high output have increased more, and accordingly, non-carbon based anode materials capable of generating an alloy with lithium, for example, silicon (Si), tin (Sn), or aluminum (Al) having a capacity of 500 mAh/g or greater that may replace the theoretical capacity of the carbon based anode material, have drawn attention.
Among the above non-carbon based anode materials, silicon has a theoretical capacity of about 4200 mAh/g that is the largest among those materials, and thus, applications of silicon are considered to be important in view of capacity. However, since silicon expands about four times greater in volume during a charging operation, an electric connection between active materials may broke or an active material may be isolated from a current collector due to a volume variation during charging and discharging processes, and an irreversible reaction such as forming of a solid electrolyte interface (SEI) may occur and lifespan may degrade because of an erosion of the active material due to an electrolyte. Therefore, there is a barrier in commercializing the silicon as the anode material.
Therefore, in order to apply a silicon material, it is necessary to restrain the volume variation during the charging and discharging and to improve an irreversible capacity of a battery. In addition, as demands for secondary batteries explosively increase, it is necessary to ensure a fabricating technology capable of massively producing silicon anode active materials.